The video of Jeremy Corbyn sitting on the floor of a train, disclosed exclusively online on 16 August, was mistakenly treated by the Guardian more as freelance journalism than what it actually was: a kind of gonzo news release by two Corbyn supporters.

The story dominated headlines in the UK for several days. It contained video of Corbyn, seated on the floor of an apparently crowded train, saying, "This is a problem that many passengers face every day, commuters and long-distance travellers. Today this train is completely ram-packed. The staff are absolutely brilliant, working really hard to help everybody. The reality is there are not enough trains, we need more of them - and they're also incredibly expensive. Isn't that a good case for public ownership?"

Almost immediately, the story began to unravel.

Readers pointed out that, in the video, Corbyn appeared to walk past empty seats. The story omitted to say that Corbyn had found a seat about 45 minutes into the journey, and that he was actually looking for a pair of seats so he could sit with his wife. Finally, Virgin trains owner Richard Branson released CCTV footage showing Corbyn walking past empty, unreserved seats on the train.

Chadwick's investigation also showed that the two authors of the story were Labour activists, not objective reporters. Freelancer Yannis Mendez was being paid by the Corbyn leadership election campaign, and "Charles B Anthony" was a fake name for his friend Anthony Casey, who "is a passionate Corbyn supporter."